The present invention relates to an adsorbent vessel containing an adsorbent to form an adsorbent bed for use in a pressure swing adsorption process wherein a cold spot forms in the adsorbent bed and/or flow to the adsorbent bed is not fully developed. More particularly, the present invention relates to such an adsorbent vessel in which a convective heat exchanger is located with the adsorbent vessel to raise the temperature of the cold spot and/or to fully develop flow to the adsorbent bed.
Pressure swing adsorption is used to produce a product gas from a multi-component gas mixture by adsorbing a component contained within the gas mixture. In a typical pressure swing adsorption process to generate oxygen, air is passed under pressure into an adsorbent formed of zeolite pellets to adsorb nitrogen and to produce a product gas composed essentially of oxygen. The adsorbent is then regenerated by desorbing nitrogen therefrom. Several interconnected adsorbent vessels containing the adsorbent are ordinarily used in carrying out the pressure swing adsorption process so that the adsorbent vessels can alternately be used to produce product or to regenerate the adsorbent.
Adsorption by the adsorbent is exothermic while desorption of the adsorbent is endothermic. If a pressure swing adsorption process were conducted to thermodynamic perfection, then the heat produced by adsorption could be used in desorption. However, adsorption does not uniformly occur in the adsorbent bed. Additionally, heat is carried away in the product gas and the desorbed gas. As a result, a cold spot forms near an inlet of the adsorption vessel and a hot spot forms near an outlet of the adsorption vessel. The adsorption capacity of some adsorbents such as zeolites, however, decreases with decreasing temperature, and therefore, the effectiveness of the adsorption decreases within the cold spot.
Another possible factor that can decrease the effectiveness of adsorption concerns the flow of the gas mixture into the adsorbent bed. For instance, if a bend or tee fitting is located too close to the inlet of the adsorbent vessel, the flow of the gas mixture will not be fully developed upon its entry into the adsorbent vessel. That is, the flow velocity will vary across the flow of the gas mixture. The disadvantage of this is that the gas mixture will be distributed on an unequal basis within the adsorbent bed and thereby decrease the degree to which the component of the gas mixture is actually adsorbed in the adsorbent bed.
The present invention provides an apparatus that has principal use in increasing the temperature of the cold spot, and therefore, decreasing the deterioration of the adsorbent capacity of the adsorbent due to the cold spot. Additionally, the present invention also provides a compact device to fully develop flow entering an adsorbent bed to insure that the gas to be separated is equally distributed throughout the adsorbent bed.